/*
 * @Date: 2021-09-10 11:16:28
 * @Author: Acckno1
 * @LastEditTime: 2021-09-10 15:28:20
 * @Description: 
 */
#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <set>
#include <bitset>
#include <utility>
using namespace std;

#define mm(a, n) memset(a, n, sizeof a)
#define mk(a, b) make_pair(a, b)

const double eps = 1e-6;
const int INF = 0x3f3f3f3f;

typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int, int> PII;
typedef pair<double, double> PDD;
typedef pair<LL, LL> PLL;
typedef pair<int, LL> PIL;

inline void quickread() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
}

int n, m;
string s;

bool is_prime(LL a) {
    for (int i = 2; i * i <= a; i ++ ) {
        if (a % i == 0) return false;
    }
    return true;
}

inline void solution() {
    cin >> n >> m;
    cin >> s;
    for (int i = 0; i + m <= s.size(); i ++ ) {
        string t = s.substr(i, m);
        LL a = stoll(t);
        if (is_prime(a)) {
            cout << t << endl;
            return ;
        }
    }
    cout << "404" << endl;
}

int main() {
    freopen("input.txt", "r", stdin);
    quickread();
    solution();
    return 0;
}